PDE4 is the major cAMP-metabolizing enzyme found in inflammatory and immune cells. PDE4 inhibitors have proven potential as anti-inflammatory drugs, especially in inflammatory pulmonary diseases such as asthma, COPD and rhinitis. They suppress the release of cytokines and other inflammatory signals and inhibit the production of reactive oxygen species. A large number of PDE4 inhibitors have been developed for a variety of clinical indications (Torphy and Page. 2000. TIPS 21, 157-159; Burnouf and Pruniaux. 2002. Curr. Pharm. Design 8, 1255-1296; Lipworth. 2005. Lancet 365, 167-175). To quote from a recent article in the British Journal of Pharmacology, “PDE4 inhibitors have been in development as a novel anti-inflammatory therapy since the 1980s with asthma and chronic obstructive pulmonary disease (COPD) being primary indications. Despite initial optimism, none have yet reached the market. In most cases, the development of PDE4 inhibitors of various structural classes, including cilomilast, filaminast, lirimilast, piclamilast, tofimilast . . . has been discontinued due to lack of efficacy. A primary problem is the low therapeutic ratio of these compounds, which severely limits the dose that can be given. Indeed, for many of these compounds it is likely that the maximum tolerated dose is either sub-therapeutic or at the very bottom of the efficacy dose-response curve. Therefore, the challenge is to overcome this limitation.” [Giembycz, Brit. J. Pharmacol. 155, 288-290 (2008)]. Many of the PDE4 inhibitors of the prior art have not reached the market because of the adverse side effect of emesis (Giembycz 2005. Curr. Opin. Pharm. 5, 238-244). Analysis of all known PDE4 inhibitors suggests that they are competitive with cAMP and bind within the active site (Houslay et al. 2005. DDT 10, 1503-1519); this may explain their narrow therapeutic ratio. The compounds of the present invention are non-competitive inhibitors of cAMP while being gene-specific inhibitors (PDE4D), and, based on the target rationale and in vitro potency, a person of skill in the art would expect the compounds to be useful as anti-inflammatory agents for the treatment, amelioration or prevention of inflammatory diseases and of complications arising therefrom and useful as CNS agents for amelioration of the cognitive decline in Alzheimer's disease, Parkinson's disease, the treatment of schizophrenia and depression, and neuroprotective in Huntington's disease.